The index closed at 1,260.34 on Aug. 3 and was at 1,237.90 on Wednesday of this week, for a net decline of 22.44 points, or 1.8 percent. But during that period, the total move of the index was more than 1,392 points, as it rose more than 684 points on good days and fell more than 707 points on bad days. That meant that the index traveled nearly 1,370 points more than it had to and that the excess volatility figure was 109 percent, the highest figure since 2009.

There were several violent swings of excess volatility during the Great Depression, but from 1940 through 1987 the figure never got as high as 100 percent."